1. Field of the Invention
The present invention relates to a switch to be mounted on various electronic devices, and more particularly to a switch comprising a switching contact section in a cavity formed in an insulative plastic case, and a metal cover covering or overlying the cavity.
2. Description of the Related Art
Recently, in connection with downsizing and weight reduction in various electronic devices, a smaller and thinner switch is preferably used in input operation sections, various detecting mechanisms and other electronic devices. Such a conventional switch will be described with reference to FIGS. 7 to 9. FIG. 7 is a perspective external view showing the conventional switch. FIG. 8 is a top view of the switch after a cover thereof has been removed, and FIG. 9 is a sectional view of the switch including the cover, taken along line II—II in FIG. 8.
The switch is generally formed in an approximately rectangular parallelepiped shape. This switch comprises an insulative plastic case 1 formed with a cavity 14 having an upward opening. The switch also includes a cover 2 formed of a thin metal sheet and joined to the case 1 so as to cover the cavity 14. The case 1 and the cover 2 define a space in the case 1, and a switching contact section is disposed in the inner space.
An operation member 3 includes an operating lever 4 and a main body 5 which are integrally molded as a single piece using resin. As shown in FIG. 8, the operation member 3 is formed with a pair of columnar protrusions 6 extending from the respective opposite sides of the main body 5, and the columnar protrusions 6 are mounted on a support portion 1A of the case 1 to serve as a pivot for allowing the operation member 3 to be rotatably held by the case 1.
The operating lever 4 protrudes obliquely upward from the front region of the case 1. When the operating lever 4 is tiltingly manipulated upward, the entire operation member 3 is rotated about the rotatably held portion described above to switch the state of the switching contact section.
The structure of the switching contact section will be described below. As shown in FIG. 8, a first contact 11 is fixed in an exposed manner to a right inner-wall constituting the cavity 14 of the case 1, and a second contact 12 is fixed in an exposed manner to a rear inner-wall of the cavity 14. The first and second contacts are led outside as a first terminal 11A and a second terminal 12A, respectively.
The reference numeral 15 indicates a movable contact segment formed of a thin metal sheet. The movable contact segment 15 is fixed to the case 1 in such a manner that a reverse C-shaped fixed portion 15 A formed at one end thereof is maintained in contact with the first contact 11.
The movable contact segment 15 has a flat plate portion 15B extending from the fixed portion 15A, and the flat plate portion 15B is resiliently bent at a given position thereof to allow the movable contract segment 15 to be contained in the cavity 14. Thus, a contact portion 15C formed at the other end of the movable contact segment 15 is in contact with the rear inner-wall surface of the case 1 while applying a resilient force of the flat plate portion 15B to the rear inner-wall surface.
FIG. 8 shows a non-operated state of the switch. In this state, the movable contact segment 15 is bent slightly rearward, and the contact portion 15C is stationarily in contact with the rear inner-wall surface of the case 1 at a position apart from the second contact 12.
The rear surface of a drive segment 17 supported by the case 1 rotatably in a horizontal direction relative to the bottom surface of the case 1 is in contact with the front surface of the flat plate portion 15B of the movable contact segment 15, and the front portion of the drive segment 17 is in contact with the main body 5 of the operation member 3, so that a forward biasing force from the movable contact segment 15 is applied to the main body 5 of the operation member 3 through the drive segment 17. This biasing force is applied in a direction allowing the operation member 3 to be rotationally moved and raised upward. When the operation member 3 is applied with the forward biasing force, the bottom surface of a stopper projection 5A formed in the rear region of the main body 5 so as to protrude rearward beyond the columnar protrusions 6 is brought into contact with a step portion 1B of the case 1. Thus, the operation member 3 is stopped at a given angular position.
The conventional switch with the above structure is operated as follows. When the operating lever 4 is pushed downward, the operating lever 4 is tiltingly rotated about the columnar protrusions 6 serving as a pivot. Then, the rear surface of the main body 5 pushes the drive segment 17 rearward, and thereby the drive segment 17 is rotationally moved toward the rear region of the case 1 in a horizontal plane. In proportion to the displacement of the drive segment 17, the front surface of the flat plate portion 15B of the movable contact segment 15 is pushed rearward. Thus, the movable contact segment 15 is resiliently bent or deformed while maintaining the fixed state of the fixed portion 15A, and the contact portion 15C is moved rightward while keeping in contact with the rear inner-wall surface of the case 1. Consequently, the contact portion 15C is brought into contact with the second contact 12 to provide a conductive state between the first contact 11 and the second contact 12, or between the first terminal 11A and the second terminal 12A, through the movable contact segment 15.
When the tilting operation force being applied to the operating lever 4 is released, the movable contact segment 15 is restored to its original shape, and the contact portion 15C is moved away from the second contact 12. Thus, the first contact 11 and the second contact 12 are returned to an electrically independent state.
During this operation, the front surface of the flat plate portion 15B of the movable contact segment 15 pushes the drive segment 17 forward so as to rotationally move the drive segment 17 in the horizontal plane. Thus, the rear surface of the main body 5 of the operation member 3 is pushed forward to its original position. The operation member 3 applied with the above force is rotated about the columnar protrusions 6 in a direction allowing the operating lever 4 to be oriented obliquely upward. Then, when the bottom surface of the stopper projection 5A formed in the main body 5 is brought into contact with the step portion 1B of the case 1, the operation lever 4 is returned to its original position where it is stopped at the angular position in the non-operated state as shown in FIGS. 7 and 8.
An example of prior art related to the invention of this application includes Japanese Unexamined Patent Publication No. 2001-184994.
In use, the above conventional switch is mounted on various electronic devices, and connected to a circuit section in a wiring board thereof. While this switch can release static electricity entering from outside through the metal thin-plate cover 2 to a grounding portion of the circuit section, there is an increasing need for developing further improved countermeasures against static electricity, from the standpoint of electronic devices using such a switch.